Hydraulic transmission assembly

ABSTRACT

The present disclosure relates to a hydraulic transmission assembly for a ground vehicle comprises a pump unit and a hydraulic motor assembly connected to the pump unit. The pump unit includes a driven shaft configured to operably connect to a motor of the ground vehicle. The hydraulic motor assembly includes a motor housing configured to rotatably mount to a wheel assembly of the ground vehicle. The housing has a central opening. A stationary output shaft has a first end section received in the central opening and a second end section configured to rigidly attach to a frame of the ground vehicle. The output shaft includes at least one internal fluid passage in fluid communication with at least one fluid passage of the pump unit. Pressurization of the hydraulic motor assembly via the pump unit rotates the motor housing relative to the stationary output shaft which, in turn, rotates the wheel assembly in one of a first direction and second direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. application Ser.No. 11/539,299, filed Oct. 6, 2006, the disclosure of which isincorporated herein by reference.

BACKGROUND

Hydraulically-controlled transmission assemblies are an efficient way ofcontrolling the speed and direction of land vehicles, such as walkbehind and ride-on lawnmowers, ATV, and tractors.

Some known hydraulically-controlled transmission assemblies include highreduction mechanical gearing that can compromise the relative smoothnessof the control of the vehicle. In addition, these transmissionassemblies may be inherently limited in the amount of ground engagingpower, and thus unable to put more than a limited amount of the engine'shorsepower into ground engaging tasks. This affects control, accuracyand longevity of the transaxle as well as compromising the vehicle'sperformance and otherwise limiting the vehicles applications.

Another known hydraulically controlled transmission assembly includes agerotor motor of the type having a spool valve that connects to a mainoutput drive shaft. The output end of the main output drive shaft isdisposed on one side of the rotor assembly and the spool valve and brakeassembly are disposed on an opposite side of the gerotor assembly. Sucha configuration requires complicated attachment of the spool valve tothe main output drive shaft and a portion of the main output drive shaftorbits and rotates. Furthermore, the spool valve includes an extensionto which brake disks are attached, thus requiring a larger housingassembly for the hydraulic device.

Other known hydraulically-controlled transmission assemblies, whichinclude a hydraulic motor and a brake assembly, typically comprise largehousings and/or complicated drive connections and/or complicated fluidpaths. Still other known ground engaging transaxles are substantial indesign and weight.

Piston-powered pumped units, while adaptable, have their ownrequirements and restrictions including the need for separate motors orthe need of an associated gear transmission to apply power to theground. While these known drive systems are functional, their compromisein cost and performance of each design is apparent.

BRIEF DESCRIPTION

In accordance with one aspect of the present disclosure, a hydraulictransmission assembly for a ground vehicle comprises a pump unit and ahydraulic motor assembly connected to the pump unit. The pump unitincludes a driven shaft configured to operably connect to a motor of theground vehicle. The hydraulic motor assembly includes a motor housingconfigured to rotatably mount to a wheel assembly of the ground vehicle.The housing has a central opening. A stationary output shaft has a firstend section received in the central opening and a second end sectionconfigured to rigidly attach to a frame of the ground vehicle. Theoutput shaft includes at least one internal fluid passage in fluidcommunication with at least one fluid passage of the pump unit.Pressurization of the hydraulic motor assembly via the pump unit rotatesthe motor housing relative to the stationary output shaft which, inturn, rotates the wheel assembly in one of a first direction and seconddirection.

In accordance with another aspect of the present invention, a hydraulicmotor assembly for use in a hydraulic transmission assembly comprises astationary output shaft and a motor housing at least partiallysurrounding the output shaft. A rotor assembly is mounted to the motorhousing. The motor housing is rotatable about the stationary outputshaft.

In accordance with yet another aspect of the present invention, ahydraulic transmission assembly comprises a rotatable housing and afixed output shaft at least partially disposed in the housing and atleast partially extending axially from the housing. The output shaftincludes first and second independently pressurizable fluid passages. Agerotor assembly cooperates with the output shaft and is incommunication with the first and second fluid passages. A pressurereleased brake assembly cooperates with the output shaft and thehousing. Pressurization of the first fluid passage rotates the housingin a first direction. Pressurization of the second fluid passage rotatesthe housing in a second direction. Pressurization of either of the firstfluid passage or the second fluid passage results in the pressurereleased brake assembly operating in a disengaged position which allowsfor rotation of the housing relative to the fixed output shaft in one ofthe first and second directions.

In accordance with still yet another aspect of the present invention, ahydraulic motor assembly comprises an output shaft including at leasttwo fluid passages. Each fluid passage is selectively and independentlypressurizable relative to the other. A motor housing at least partiallysurrounds the output shaft. A rotor assembly is operably connected tothe motor housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a hydraulic transmissionassembly.

FIG. 2 is a partial enlarged view of the hydraulic transmission assemblyof FIG. 1.

FIG. 3 is a cross-sectional view of the hydraulic transmission assemblyof FIG. 1, the cross section being taken generally along lines 3-3.

FIG. 4 is a partial enlarged view of the hydraulic transmission assemblyof FIG. 3.

FIG. 5 is a partial cross-sectional view of a hydraulic transmissionassembly in accordance with another aspect of the present invention.

FIG. 6 is an enlarged partial cross-sectional view of the hydraulictransmission assembly of FIG. 5, the cross section being taken generallyalong lines 6-6.

FIG. 7 is an enlarged partial cross-sectional view of the hydraulictransmission assembly of FIG. 5.

DETAILED DESCRIPTION

It should, of course, be understood that the description and drawingsherein are merely illustrative and that various modifications andchanges can be made in the structures disclosed without departing fromthe scope and spirit of the invention. It will also be appreciated thatthe various identified components of a hydraulic transmission assemblydisclosed herein are merely terms of art that may vary from onemanufacturer to another and should not be deemed to limit the presentinvention. All references to direction and position, unless otherwiseindicated, refer to the orientation of the hydraulic transmissionassembly illustrated in the drawings.

Referring now to the drawings, wherein like numerals refer to like partsthroughout the several views, FIGS. 1-4 illustrate partialcross-sectional views of the hydraulic transmission assembly 10 inaccordance with one aspect of the present invention. The hydraulictransmission assembly 10 for a ground vehicle, for example a ridingzero-turn mower, a walk-behind commercial lawn mower, garden tractor, anall-terrain vehicle, or a small self-contained tracked backhoe, uses acombination of components to provide a reliable, smooth, easy tocontrol, high-torque power delivery package. Power input, control, andpower delivery are apparent to the user. The hydraulic transmissionassembly 10 generally includes a pump unit 12, a hydraulic motorassembly 14 and a brake assembly 16.

The pump unit 12, which in the depicted embodiment is a variabledisplacement pump unit, includes a pump housing 22 and a driven shaft 24that is driven by a motor M (FIG. 1, depicted schematically) that isexternal to the hydraulic transmission assembly 10. The motor M can bethe motor that drives the vehicle as well as other components of thevehicle, for example mower blades, and the like. The motor M canoperatively drive the driven shaft 24 through a transmission (notshown).

As best illustrated in FIGS. 1 and 2, a rotatable cylinder block 30connects to the driven shaft 24 so that the block 30 rotates with theshaft. The rotatable cylinder block includes a plurality of chambers 32that receive spring loaded pistons 38. A swash plate (not shown)contacts the pistons 38 to vary the pump chamber volume in each chamber32. The swash plate pivots about the rotational axis of the driven shaft24. Upper and lower bearings can support the driven shaft. Angularadjustment of the swash plate can be controlled by a control member (notshown). The operator of the ground vehicle can alter the volumetricoutput of each individual pump by manipulating the control member in amanner that is known in the art.

As more clearly seen in FIGS. 3 and 4, the pump housing 22 includes aplurality of passes and openings. First and second curved openings 40and 42 respectively communicate with the chambers 32 of the cylinderblock 30 to provide input and output ports for the pump unit 12depending on the direction of rotation of the driven shaft 24. The firstcurved opening 40 communicates with a first linear passage 50 (shown inphantom) that communicates with the hydraulic motor assembly 14 in amanner that will be described in more detail below. The second curvedopening 42 communicates with a second linear passage 52 (shown inphantom) that communicates with the hydraulic motor assembly 14 in amanner that will be described in more detail below. A first opening 56is formed in a first planar surface 58 of the housing 22 where the firstlinear passage terminates. A second opening 60 is also formed in thefirst planar surface of the housing and communicates with the secondlinear passage 52.

With reference back to FIGS. 1 and 2, the pump unit 12 can be connectedto a frame F of the ground vehicle via conventional manners. In thedepicted embodiment, first and second bolt openings 64 and 66,respectively, formed in the housing 22, are in registry with first andsecond bolt openings 68 and 70, respectively, formed in the frame. Thecorresponding bolt openings allow the pump unit 12 to attach to theframe.

With particular reference to FIGS. 3 and 4, the pump unit 12 is furtherconnected to a manifold 74. The manifold includes a planar first surface76 that contacts the first planar surface 58 of the pump unit housing 22when the hydraulic transmission assembly 10 is finally assembled. Theplanar surfaces can take other complementary configurations. Themanifold 74 also includes a second planar surface 78 opposite the firstplanar surface. The second planar surface can attach to the frame F viaconventional manners. A first passage 80 (shown in phantom) communicateswith first linear passage 50 of the pump unit 12. The first passage 80extends from the first planar surface 78 through the manifold to a firstport 82 of an output shaft 86 of the hydraulic motor assembly 14. Thefirst passage 80 is in fluid communication with a rotor assembly 90attached to the hydraulic motor assembly via a first axially alignedoutput shaft passage A in a manner that will be described in more detailbelow.

The manifold 74 also includes a second passage 92 (shown in phantom inFIGS. 3 and 4) that contacts the first planar surface 58 of the pumpunit housing 22 when the hydraulic transmission assembly 10 isassembled. The second passage 92 communicates with the second linearpassage 52 of the pump unit 12. The second passage 92 extends from thefirst planar surface 78 through the manifold to a second port 96 of theoutput shaft 86 of the hydraulic motor assembly 14. The second passage92 is also in fluid communication with the rotor assembly 90 via asecond axially aligned output shaft passage B in a manner that will bedescribed in more detail below.

Conventionally, an output shaft of a hydraulic motor assembly isrotatably configured to drive a wheel of a ground vehicle. In thedepicted embodiment of FIGS. 1-4, the output shaft 86 is generally fixedto the frame F of the ground vehicle. A first end portion 100 of theoutput shaft extends through an opening 102 in the frame F and isreceived in an opening 104 of the manifold 74. The first end portion canbe secured to the frame via conventional manners, such as a snap ring106 (FIG. 2), and can be connected to the manifold via bolt openings 107(FIG. 2) formed in the A first end portion 100, which align with boltopenings (not shown) formed in the manifold. A second end portion 108 ofthe output shaft 86 extends through an opening 112 (FIG. 4) located in amotor housing 110 of the hydraulic motor assembly 14 and is coupled tothe rotor assembly 90.

The motor housing 110 includes a front housing section 120 and a rearhousing section 122. The housing sections attach to one another viabolts (not shown) received in bolt holes (not shown) formed in thehousing sections. The rear housing section 122 is attached to a drum (orhub) D of a wheel W of the ground vehicle via bolts 130 received in boltholes 132 and 134 formed in the respective second housing section andthe drum. As will be described in greater detail below, the motorhousing is configured to rotate relative to the fixed output shaft 86 asone of the first and second axially aligned fluid passages A and B ispressurized. This, in turn, drives the wheel of the ground vehicle in aforward or reverse direction depending on which passage is pressurized.

With particular reference to FIGS. 2 and 4, the rotor assembly 90, whichis similar to a known gerotor assembly, includes a stator 140 (which canalso include rollers) and a rotor 142. The rotor includes a plurality ofteeth that cooperate with the stator in a known manner to defineexpanding fluid pockets and contracting fluid pockets as the rotorrotates and orbits relative to the stator when hydraulic fluid isdirected toward the expanding pockets.

A wobble stick 146, also referred to as a drive link or a wobble shaft,connects to the rotor 142 at a first end 150. The wobble stick canattach to the rotor via a splined connection, which is known in the art.The first end 150 of the wobble stick 146 rotates and orbits relative tothe stator 140 as the rotor 142 rotates and orbits relative to thestator. A second end 152 of the wobble shaft is received in the outputshaft 86. Particularly, the output shaft 86 includes a central opening156 for receiving the second end of the wobble stick.

A wear plate 160 is sandwiched between the rear housing section 122 andthe rotor assembly 90. The wear plate includes a plurality of openings162 radially spaced from the rotational axis of the motor housing 110.The openings 162 in the wear plate 50 communicate with the pockets(either expanding or contracting) formed in the rotor assembly 90 in amanner that is known in the art. Accordingly, the number of openings 162generally equals the number of pockets.

The rotor assembly 90 is rotatably connected to the motor housing 110 toimpart rotation to the motor housing and, in turn, the wheel.Particularly, rotation of the motor housing 110 about a rotational axisis caused by delivering pressurized fluid to the expanding cells of therotor assembly 90. In the depicted embodiment, a rotor housing 164 (FIG.2) is attached to the rear housing section 122 via conventional manners,such as bolts which can extend through aligned openings located in therotor housing, wear plate and rear housing section. An end plate (notshown) can attach to the rotor assembly 90 on an opposite side of therotor assembly as the wear plate 160.

The hydraulic transmission assembly 10 further includes the brakeassembly 16 that can inhibit the motor housing 110 from rotating whenthe hydraulic motor assembly 14 is in an unpressurized condition.

With reference back to FIG. 4, pressurized fluid travels through a thirdpassageway C, which will be described in more detail below, topressurize a brake chamber 172 that is at least partially defined in themotor housing 110. In the depicted embodiment, passageway C is axiallyaligned with first and second passageways A and B. No matter which port,either first port 82 or second port 96, serves as an inlet for thehydraulic motor assembly 14, the brake chamber 100 is pressurized viathe third passageway C. This is due, at least in part, to a shuttlevalve 180.

The brake assembly 16 for the hydraulic transmission assembly will bedescribed in more detail. With reference to FIGS. 2 and 4, the outputshaft 40 includes a splined portion 184 that receives friction disks 186that are appropriately shaped so that the friction disks rotate alongwith the motor housing 110. Disk stampings 188 attach to the fronthousing section 120 in a known manner so that the disk stampings do notrotate with respect to the motor housing 110. The brake package, i.e.,the friction disks and the disk stampings, are disposed forwardly of therotor assembly 90.

In the depicted embodiment, a piston 190 contacts one of the frictiondisks 186. Alternatively, the piston 190 can contact one of the diskstampings 188 if the orientation was slightly changed. A seal 192contacts the piston and the front housing section 120 thus separatingthe brake chamber 172 from a cavity 194 that receives a biasing member,for example a spring 196, that urges the piston 190 towards the frictiondisk. When the brake chamber is unpressurized the spring urges thepiston towards the friction disk and the friction disks contact the diskstampings thereby inhibiting the rotation of the motor housing 110.

A thrust bearing assembly 200, which in the depicted embodiment includestwo washers having a thrust bearing sandwiched between them, surroundsthe output shaft 86 at a location that is aligned with a radial passage202 of the output shaft. A seal retainer 206 that retains a dynamic seal208 fits around the output shaft outside of the thrust bearing assembly200. A dust cover (not shown) can be fitted around the output shaft toprotect the seal and other internal components. The seal 208 cooperateswith the front housing section 120, the seal retainer 206 and the outputshaft 86 to define a boundary of the brake chamber 172.

Pressurized fluid passes through the thrust bearing assembly 200, whichcan act as a sort of miniature pump, to pressurize the brake chamber172. When pressurized, the fluid acts on the piston 190 urging it awayfrom the friction disks 186. The hydraulic transmission assembly 10 canbe a “bearingless” device in that the depicted embodiment does notinclude bearings, other than the thrust bearing assembly. In abearingless hydraulic device, the output shaft can include a knurledsurface.

With reference to FIGS. 1 and 3, the operation of the hydraulictransmission assembly will now de described. In this example, rotationof the driven shaft 24 of the pump unit 12 in a first directionpressurizes the first axially aligned passage A. This, in turn, rotatesthe motor housing 110, which rotates the drum D and wheel W of theground vehicle in a first or forward direction. Particularly, the pumpunit 12 delivers pressurized fluid through the curved opening 40 and thefirst linear passage 50 of the pump unit, through the first passage 80of the manifold 74 and into a first annular groove 220 formed in themanifold. The first annular groove communicates directly with the firstport 82 of the output shaft 86. The pressurized fluid flows into thefirst port and through a first radially aligned passage 222, which is influid communication with a first end section 224 of the first axiallyaligned passage A. Fluid flows through the first axially aligned passagetoward the rotor assembly 90. A second end section 226 of the firstaxially aligned passage A is in fluid communication with a secondradially aligned passage 230, which directs the pressurized fluid to asecond annular groove 232 formed in the rear housing section 122 of themotor housing 110.

A first predetermined volume of the fluid flows from the second annulargroove into a first annular slot 234, which extends toward the rotorhousing 90. A second predetermined volume of the fluid flows into asecond annular slot 236, which extends toward the pump unit 12. Thefirst and second annular slots are formed in the rear housing section122. The first annular slot 234 selectively communicates with axialslots 240 formed in the output shaft 86. Generally axially alignedpassages 246 (one shown in FIG. 1) extend between the axial slots andthe appropriate openings 162 in the wear plate 160.

Fluid enters the pockets in the rotor assembly 90 via the openings 162in the wear plate 160 on one side of a line of eccentricity and exitsthe rotor assembly via openings 162 in the wear plate 160 on theopposite side of the line of eccentricity. As pressurized fluid flowsinto the rotor assembly via the openings 162, the pressurized fluid isdelivered to the expanding cells of the rotor assembly, which causes therotor assembly to rotate in the first direction. As indicatedpreviously, the rotor assembly 90 is connected to the motor housing 110,which is attached to the drum of the wheel, and the output shaft 86 isfixed to the vehicle frame F. Thus, as the rotor assembly rotates in thefirst direction, the motor assembly and, in turn, the wheel, rotate inthe first direction.

A second annular slot 250 formed in the output shaft 86 receives theflow of fluid exiting the rotor assembly 90. A second radially alignedpassage 252 also formed in the output shaft 86, which is incommunication with the second annular slot 250, directs the fluid into asecond end section 258 of the second axially aligned passage B. Fluidflows through the second axially aligned passage B toward the pump unit12. The fluid can then directed back into the pump unit via a secondannular groove 260 formed in the manifold, which is in communicationwith a first end section 262 of the second axially aligned passage B, afirst end section 264 of the third axially aligned passage C and thesecond manifold passage 92. Alternatively, the fluid can be directedinto a fluid tank (not shown) which communicates with the pump unit.

As indicated before, the second predetermined volume of the fluid flowsfrom the second annular groove 232 into the second annular slot 236.This pressurized fluid flows into a third radially aligned passage 270formed in the output shaft 86. The third radially aligned passagecommunicates with both the second end section 258 of the second axiallyaligned passage B and a first end section 272 of the third axiallyaligned passage C. Operably located in the third radially alignedpassage 270 is the shuttle valve 180; although, it should be appreciatedthat other types of valves are also contemplated. As the pressurizedflows through the third radially aligned passage 270 to the thirdaxially aligned passage C, the pressurized fluid moves the shuttle valveto a first location, which precludes fluid from passing from the thirdradially aligned passage 270 into the second axially aligned passage B.The pressurized fluid is directed into the third axially aligned passageC and is at least partially delivered to the brake chamber 172, thusdisengaging the brake assembly 16. Fluid travels into the radial passage202, through the thrust bearing assembly 200, which can act as a sort ofminiature pump, to pressurize the brake chamber 172. When pressurized,the fluid acts on the piston 190 urging it away from the friction disks186. The remainder of this pressurized fluid flows through the thirdaxially aligned passage C and back into one of the pump unit and fluidtank via the second annular groove 260.

With continued reference to FIGS. 1 and 3, pressurization of the secondaxially aligned passage B rotates the motor housing 110 and, in turn thedrum D and wheel W of the ground vehicle, in a second or reversedirection.

Particularly, the pump unit 12 delivers pressurized fluid through thecurved opening 42 the second linear passage 52 of the pump unit, throughthe second passage 92 of the manifold 74 and into the second annulargroove 260 formed in the manifold. The second annular groovecommunicates directly with the second port 96 of the output shaft 86.The pressurized fluid flows through the second port and at leastpartially into both of the first end sections 262 and 264 of the secondand third axially aligned passages B and C, respectively.

Pressurized fluid flowing through the second axially aligned passage Bis directed towards the rotor assembly 90. At least a portion of thepressurized flowing through the third axially aligned passage C, whichis also in communication with the second annular groove 260, isdelivered to the brake chamber 172, thus disengaging the brake assembly,as described above. The remainder of the pressurized fluid flows towardsthe third radially aligned passage 270. As the pressurized flows intothe third radially aligned passage 270, the pressurized fluid moves theshuttle valve 180 to a second location, which precludes fluid frompassing from the third radially aligned passage 270 into the secondannular slot 236. In this regard, the fluid is directed into the secondaxially aligned passage B.

Fluid flows through the second axially aligned passage, the secondradially aligned passage 252, the second annular slot 250 and enters thepockets in the rotor assembly 90 via the openings 162 in the wear plate160 on one side of a line of eccentricity. As pressurized fluid flowsinto the rotor assembly via the openings 162, the pressurized fluid isdelivered to the expanding cells of the rotor assembly, which causes therotor assembly to rotate in the second direction, which, in turn,rotates the motor assembly and the wheel in the second direction. Fluidexits the rotor assembly via openings 162 in the wear plate 160 on theopposite side of the line of eccentricity.

Fluid travels through the axially aligned passages 246, the firstannular slot 234, the second annular groove 232, and into the firstaxially aligned passage A. Although some fluid may flow into the secondannular slot 236 and third radially aligned passage 270, that fluid flowis stopped by the shuttle valve 180. Fluid flows through the firstaxially aligned passage A toward the pump unit 12. The fluid can then bedirected back into the pump unit via the first annular groove 220 andthe first manifold passage 82. Alternatively, the fluid can be directedinto the fluid tank.

It should be appreciated that the rotational axis of the motor housing110 is at least generally perpendicular to the rotational axis of thedriven shaft 24 of the pump unit 12. Such a configuration allows for avertical drive shaft of the motor M, which is almost universallypreferred for mowers.

An alternate embodiment of a hydraulic transmission assembly is shown inFIGS. 5-7. Since most of the structure and function is substantiallyidentical, reference numerals with a single primed suffix (′) refer tolike components (e.g., hydraulic transmission assembly is referred to byreference numeral 10′), and new numerals identify new components in theadditional embodiment of FIGS. 5 and 6.

Similar to the previous embodiment, the hydraulic transmission assembly10′ generally includes a pump unit 12′ connected to a hydraulic motorassembly 14′ and a brake assembly 16′. The hydraulic transmissionassembly can be connected to a frame F′ of the ground vehicle viaconventional manners. The pump unit includes first and second linearpassages 50′ and 52′, respectively, in fluid communication with firstand second passages 300 and 302, respectively, formed in a manifold 308.

The hydraulic motor assembly 14′ comprises a rotatable motor housing310, a stationary output shaft 312 and a rotor assembly 90′ rotatablycoupled to the motor housing. The output shaft can be fixed to the frameF′ and the manifold 308 The output shaft includes first, second andthird axially aligned passages (the first passage A′ is shown in FIG. 5and the second and third passages B′ and C′, respectively, are shown inFIG. 6). The motor housing is configured to rotate relative to the fixedoutput shaft 312 as one of the first and second axially aligned fluidpassages A′ and B′ is pressurized via the pump unit 12′. The thirdaxially aligned passage C′ directs fluid to the brake assembly 16′ topressurize a brake chamber 320 and release a single brake plate 322. Nomatter which axially aligned fluid passage is pressurized, either thefirst or the second, the brake chamber 320 is pressurized. This is due,at least in part, to a shuttle valve 180′ which allows selectivecommunication between the pressurized first or second axially alignedfluid passage and the third axially aligned passage.

The motor housing includes a front housing section 330 and a rearhousing section 332. The housing sections can attach to one another viaconventional manners. The rear housing section 332 is attached to a drumD′ of a wheel W′ of a ground vehicle via conventional manners. The motorhousing is configured to rotate relative to the fixed output shaft 312as one of the first and second axially aligned fluid passages ispressurized. This, in turn, drives the wheel of the ground vehicle in aforward or reverse direction.

The third passage C′ includes a first end section 344 having a firstdimension and a second end section 346 having a second smallerdimension. The first end section is in fluid communication with a fluidtank (not shown) via a tank dump 348 formed in the manifold 308. Thesecond end section is in fluid communication with one of the first andsecond axially aligned passages via the shuttle valve 180′. Located inthe enlarged first end section 344 is a relief valve 350.

The relief valve generally includes a stopper 356, a spring 358 forbiasing the stopper against an opening 360, a body 362 including apassage 364 in communication with the tank dump 348 and a hollowthreaded portion 364. The stopper 356 includes a through hole 368 whichallows fluid to flow to the tank dump and/or a heat exchanger orradiator R (schematically depicted in FIG. 6). Passing fluid through theheat exchanger allows dissipation of heat which is generally desirablefor hydraulic systems of this type and provides for a stable hydraulicsystem. The hole diameter is typically dependent upon the type ofvehicle. Generally, the hole 368 has a diameter of approximately 0.003inches to approximately 0.015 inches.

The spring 358 is compressed between the stopper and the body. Thethreaded portion can have external threads that engage internal thread370 formed in a portion of the manifold 308 for securing the reliefvalve in the first end section. Alternatively, the relief valve 350 cansecured in the third passage C′ in other manners, such as a press infit. In such instance, the relief valve may not be threaded. The stopperincludes a rounded contact surface adapted to prevent fluid flow fromentering the first end section 344.

The relief valve protects the components of the hydraulic transmissionassembly 10′ from a pressure surge. For example, rotation of a drivenshaft 24′ of the pump unit 12′ in a first direction pressurizes thefirst axially aligned passage A′. In this regard, the second axiallyaligned passage B′ acts as a fluid return passage. If the motor housing310 suddenly stops rotation, e.g. from suddenly contacting anobstruction, while pressure fluid is being delivered to the firstaxially aligned passage, the hydraulic transmission assembly wouldexperience a pressure spike. As the pressure in the second end section346 of the third passage C′ exceeds the biasing force of the spring 358,which can be set at a number of different pressures, the spring 358 willcompress. This will move the stopper 356 away from the opening 360allowing fluid to flow into the first end section 344, around the springand into passage 364. The fluid is then delivered into the tank dump 348and/or radiator R which reduces the pressure in the hydraulictransmission assembly. Once the pressure in the second end section 364returns below the biasing force of the spring, the spring will move thestopper back against the opening 360.

Similar to the first embodiment, rotation of the driven shaft 24′ of thepump unit 12′ in a first direction pressurizes the first axially alignedpassage A′. This, in turn, rotates the motor housing 310 in a firstdirection, which rotates the wheel assembly of the ground vehicle in afirst or forward direction. Rotation of the driven shaft 24′ of the pumpunit 12′ in a second direction pressurizes the second axially alignedpassage B′. This, in turn, rotates the motor housing 310 in a seconddirection, which rotates the wheel assembly of the ground vehicle in asecond or reverse direction. However, unlike the first embodiment,pressurized fluid is delivered to the third axially aligned passage C′via a radially aligned passage 380. As the pressurized flows into theradially aligned passage 380, the pressurized fluid moves the shuttlevalve 180′, which precludes fluid from passing from the radially alignedpassage into the first axially aligned passage.

With reference to FIG. 7, alternate manners of disengaging or releasingthe brake assembly 16′ during a static condition of the hydraulictransmission assembly 10′ is illustrated.

In a first manner, a shut-off valve 400, which is coupled to themanifold 308, is in selective communication with the first and secondpassages 300 and 302, respectively, formed in the manifold. In use, theshut-off valve prevents flow of fluid to the pump unit 12′ therebymaintaining fluid in the axially aligned passages. To release the brakeassembly, an external pump 404, which is in communication with a fluidreservoir 406, is connected to the shut-off valve. The external pumppressurizes the fluid in one of the first and second axially alignedpassages A′ and B′, respectively, which pressurizes the fluid in thethird axially aligned passage C′. At least a portion of the pressurizedfluid is directed through the thrust bearing assembly 200′ to pressurizethe brake chamber 172′, as described above. As the brake chamber ispressurized, the brake assembly is released which allows the motorhousing 310 to rotate relative to the stationary output shaft 312.

In a second manner, bolts 420 can extend through bolt holes 422 locatedin the rear housing section 332 through a cavity 430 that receives abiasing member, for example a spring 432. A threaded portion of eachbolt threadingly engages an aperture 434 located in a piston 436.Similar to the first embodiment, the spring urges the piston 436 towardsthe single brake plate 322. When the brake chamber is unpressurized, thespring urges the piston towards the brake plate which contact the fronthousing section 330 thereby inhibiting the rotation of the motor housing310. To disengage the brake assembly, the bolts are rotated, which, inturn, moves the piston towards the rear housing section. As the pistonmoves, the spring compresses thereby releasing the single brake plate322 and allowing the motor housing to rotate.

As to a further discussion of the manner of operation of the alternateembodiment of the hydraulic transmission assembly 10′, same should beapparent from the above description relative to the first embodiment.Accordingly, no further discussion will be provided.

The above disclosed hydraulic transmission assembly provides all ornearly all of the fluid passages for the transmission assembly insiderobust housings. This differs from transmission assemblies that includeintervening hoses between the pump unit and the hydraulic motorassembly. As discussed above, fluid communication between the pump unitand the hydraulic motor assembly is provided by internal fluid passageshaving no intervening hoses. Such a configuration reduces fluid leakageand provides a more efficient delivery of fluid. The assembly isprovided in a manner so that components of the assembly can be easilyinterchanged. For example, many different hydraulic motor assemblies canattach to the pump unit. All of the components of the hydraulictransmission assembly can be mounted to one another and thereforemounted as one unit to the ground vehicle. Such a configuration enhancesthe structural and rotational integrity of the power input and alsosimplifies the remainder of the ground vehicle to which the transmissionis to be mounted. Attaching the motor housing to the drum of the wheel,as opposed to the output shaft being attached to the drum, utilizesspace in the vehicle that was once not utilized. Accordingly, thehydraulic transmission assembly can be used with vehicles that were oncethought too small to incorporate such a hydraulic transmission.

The present disclosure has been described with reference to severalembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. For example, it should be appreciated that one-way checkvalves, which are in selective communication with the first and secondaxially aligned passages, can be implemented in lieu of the thirdaxially aligned passage to pressurized the brake chamber. It is intendedthat the disclosures be construed as including all such modificationsand alterations insofar as they come within the scope of the claimsappended hereto, as well as their equivalents.

1. A hydraulic transmission assembly for an associated ground vehiclecomprising: a pump unit configured to operably connect to an associatedmotor of the associated ground vehicle; a manifold fluidly connected tosaid pump unit, the manifold including means for mounting to theassociated ground vehicle; and a hydraulic motor assembly connected tosaid manifold, said motor assembly including: a motor housing configuredto rotatably mount to an associated wheel assembly of the associatedground vehicle, a stationary output shaft having a first end sectionreceived in said motor housing and a second end section configured torigidly attach to an associated frame of the associated ground vehicle,said output shaft including at least one internal fluid passage in fluidcommunication with at least one fluid passage of said pump unit, whereinpressurization of said hydraulic motor assembly via said pump unitrotates said motor housing relative to said stationary output shaftwhich, in turn, rotates the associated wheel assembly in one of a firstdirection and second direction.
 2. The hydraulic transmission assemblyof claim 1, wherein said output shaft includes a first defined fluidpassage and a second defined fluid passage, each of said first andsecond defined fluid passage being in fluid communication with said atleast one fluid passage of said pump unit, wherein pressurization ofsaid first defined fluid passage rotates said motor housing in saidfirst direction, wherein pressurization of said second defined fluidpassage rotates said motor housing in said second direction.
 3. Thehydraulic transmission assembly of claim 2, wherein said output shaftincludes a third defined fluid passage in selective fluid communicationwith one of said first and second defined fluid passages, said thirddefined fluid passage communicating with a pressurizable brake assemblyat least partially housed in said hydraulic motor assembly.
 4. Thehydraulic transmission assembly of claim 3, further including a valvemember, said valve member allowing selective communication betweeneither of said first defined fluid passage or said second defined fluidpassage, when either of said first or second passages are pressurized,and said third defined fluid passage.
 5. The hydraulic transmissionassembly of claim 1, further comprising a rotor assembly fixedly mountedto said motor housing, said rotor assembly including at least one fluidpassage in communication with said at least one internal fluid passageof said output shaft.
 6. The hydraulic transmission assembly of claim 1,wherein said manifold is fluidly connected to said at least one passageof said pump unit and said at least one passage of said output shaft viaat least one internal passage, wherein said manifold fluidly connectssaid pump unit and said hydraulic motor assembly with no interveningexternal fluid lines.
 7. A hydraulic motor assembly for use in anassociated hydraulic transmission assembly, said hydraulic motorassembly comprising: a stationary output shaft; a motor housing at leastpartially surrounding said output shaft; and a rotor assembly mounted tosaid motor housing, wherein said motor housing is rotatable about saidstationary output shaft, wherein said motor housing at least partiallydefines a pressurizable brake chamber, said output shaft includes atleast one pressurizable fluid passage in fluid communication with saidbrake chamber.
 8. The hydraulic motor assembly of claim 7, wherein saidoutput shaft includes a first pressurizable fluid passage and secondseparate pressurizable fluid passage, wherein pressurization of saidfirst fluid passage rotates said motor housing in a first direction,wherein pressurization of said second fluid passage rotates said motorhousing in a second direction.
 9. The hydraulic motor assembly of claim8, wherein said output shaft includes a third separate pressurizablefluid passage in fluid communication with said brake chamber, whereinsaid third fluid passage is in selective communication with one of saidfirst and second fluid passages via a valve member.
 10. The hydraulicmotor assembly of claim 9, further including a second valve member, saidsecond valve member operably coupled to said third fluid passage, saidsecond valve member configured to direct pressurized fluid out of saidhydraulic motor assembly in response to a pressure surge.
 11. Thehydraulic motor assembly of claim 7, in connection with a wheel drum,said motor housing being connected to said wheel drum for rotationtherewith.
 12. A hydraulic transmission assembly comprising: a rotatablehousing; a fixed output shaft at least partially disposed in saidhousing, said output shaft including first and second independentlypressurizable fluid passages; a rotor assembly cooperating with saidoutput shaft, said rotor assembly being in communication with said firstand second fluid passages; and a pressure released brake assemblycooperating with said output shaft and said housing, whereinpressurization of said first fluid passage rotates said housing in afirst direction, wherein pressurization of said second fluid passagerotates said housing in a second direction, and wherein pressurizationof either of said first fluid passage or said second fluid passageresults in said pressure released brake assembly operating in adisengaged position which allows for rotation of said housing relativeto said fixed output shaft in one of said first and second directions.13. The hydraulic transmission assembly of claim 12, wherein saidhousing includes a first housing section mounted to a second housingsection, said first and second housing sections defining a pressurizablebrake chamber for housing said pressure released brake assembly.
 14. Thehydraulic transmission assembly of claim 13, wherein said output shaftfurther includes a third fluid passage in communication with said brakechamber, wherein pressurization of either of said first fluid passage orsaid second fluid passage results in pressurization of said third fluidpassage.
 15. The hydraulic transmission assembly of claim 14, furtherincluding a valve member, said valve member allowing selectivecommunication between either of said first fluid passage or said secondfluid passage, when either of said first or second passages arepressurized, and said third fluid passage.
 16. The hydraulictransmission assembly of claim 14, further including a relief valvemember for relieving a pressure build-up in said hydraulic transmissionassembly, wherein said relief valve member includes a fluid leakagehole, said leakage hole allowing fluid to flow to at least one of a tankdump and a heat exchanger for dissipation of heat.
 17. The hydraulictransmission assembly of claim 12, further comprising means fordisengaging said brake assembly during a static condition of saidhydraulic transmission assembly.
 18. The hydraulic transmission assemblyof claim 12, wherein said pressure released brake assembly includes afirst brake disk and a second brake disk, said first brake disk beingconnected to said output shaft and said second brake disk beingconnected to said housing.
 19. The hydraulic transmission assembly ofclaim 18, further comprising: a piston disposed in said housing adjacentat least one of the first and second brake disks, the piston cooperatingwith said housing to at least partially define a brake pressure chamber,the housing and the first and second passages being configured such thatpressurization of either passage results in pressurization of said brakepressure chamber; and a biasing member disposed in said housing andcontacting said piston, said biasing member urging said piston toward atleast one of the first and second brake disks.
 20. The hydraulictransmission assembly of claim 12, wherein said rotor assembly is agerotor assembly including a rotor and a stator, and further comprisinga drive link having a first end and a second end, said first end beingconnected to said rotor, said second end being connected to said outputshaft, wherein said housing receives said gerotor assembly and saiddrive link.
 21. A hydraulic transmission assembly for an associatedground vehicle comprising: a pump unit; a hydraulic motor assemblyfluidly connected to said pump unit, said motor assembly including: arotatable housing configured to connect a wheel assembly of theassociated ground vehicle; and an output shaft at least partiallydisposed in said housing and configured to secure a frame of theassociated ground vehicle, said output shaft including first and secondindependently pressurizable fluid passages in fluid communication withsaid pump unit; wherein pressurization of at least one of said first andsecond passages via said pump unit rotates said motor housing relativeto said output shaft which, in turn, rotates the wheel assembly in oneof a first direction and second direction; a radiator fluidly connectedto said hydraulic motor assembly; and a valve in the hydraulic motorassembly configured to allow fluid to flow to said radiator fordissipation of heat while maintaining pressure in at least one of thefirst and second passages.
 22. The hydraulic transmission assembly ofclaim 21, wherein said motor housing at least partially defines apressurizable brake chamber for at least partially housing a pressurereleased brake assembly, wherein said output shaft includes a thirddefined fluid passage in selective fluid communication with one of saidfirst and second defined fluid passages, said third defined fluidpassage communicating with said brake assembly.
 23. The hydraulictransmission assembly of claim 22, wherein said valve is operablycoupled to said third fluid passage.
 24. The hydraulic transmissionassembly of claim 23, wherein said valve includes: a stopper including athrough hole for allowing fluid to flow to said radiator, and a biasingmember for biasing the stopper against an opening of said third fluidpassage.
 25. The hydraulic transmission assembly of claim 22, whereinsaid valve is disposed in said third passage.